The overall objective of this research is to elucidate the neural mechanisms underlying two "higher" behavioral phenomena in the marine mollusk Pleurobranchaea: choice (which is a reflection of behavioral hierarchies) and associative learning. The work proposed in the present application is aimed at understanding one aspect of the behavioral hierarchy, namely, the suppression of feeding during egg laying. Isolated nervous systems will be bathed in crude extract containing egg laying hormone, and in a solution of the purified hormone, to confirm in vitro hormonal suppession of the feeding motor program. If successful, these experiments will be followed by intracellular analysis of select identified neurons and classes of neurons to determine where in the network the hormonal suppression occurs, and to elucidate the biophysical mechanisms underlying the suppression. Simultaneously, the neural organization of the paracerebral command neuron population will be undertaken. In addition, coordinated behavioral and neural analysis of the interaction between feeding behavior and withdrawal behavior will be continued. Specifically, we will test the hypothesis that the inhibition between the respective motor networks is reciprocal rather than undirectional.